This Solar-Powered Device Pulls Drinking Water From the Driest Desert Air
Thanks to a team of researchers, the world is one step closer to Star Wars-style moisture farming. A spongelike device uses solar energy to suck water vapor from the air, even in the lowest humidity. The team -- a combination of researchers from UC Berkely and MIT -- developed a way to pull nearly 3 liters of water per day per kilogram of absorber used.
[Image Source: MIT via Hyunho Kim]
The team estimates nearly 13 trillion liters of water are floating through Earth's atmosphere at any one point in time. That's 10 percent of all the freshwater found in the planet's lakes and rivers. For decades, groups have attempted to condense the water vapor and trap it for use. However, typically those systems require more energy than what they're worth or they require extremely humid air. This bicoastal team of researchers wanted to remedy both of those issues.
Led by Omar Yaghi with UC Berkeley, the researchers looked at crystalline powders called metal organic frameworks (MOFs). Yaghi developed the world's first MOF over 20 years ago. The porous crystal structures come together like a Tinkertoy set. Metal atoms serve as a hub and stick-like organic compounds link those metal atoms together. Yaghi created those structures to be flexible to a chemist's needs. Researchers can adjust the properties on each MOF to control the strength of the bonds.
Illustration of the MOF structure [Image Source: Berkeley Labs]
"By carefully designing this material, we can have surface properties that can absorb water very efficiently at 50 percent humidity, but with a different design, it can work at 30 percent," said MIT graduate student Hyunho Kim. "By selecting the right materials, we can make it suitable for different conditions. Eventually, we can harvest water from the entire spectrum" of concentrations.
Since Yaghi developed MOFs 20 years ago, over 20,000 MOFs have been synthesized with different molecular properties and structures. The spongey configuration can become hydrophilic and attract water with a high surface area. The team also noted that when the material gets placed on a black surface to absorb solar heat and a lower surface is kept at the same temperature as the outside air, water can be cooled and drop down to collect onto that lower surface.
The MOF sheet is placed between a solar absorber and condenser plate inside the chamber. The team opens the chamber at night to let surrounding air flow through the MOF and cool the water molecules. During the day, the chamber is closed and sunlight heats the chamber. The molecules get heated and driven toward the condenser.
[Image Source: MIT via Hyunho Kim]
The team wants to continually improve and tweak the MOF structure in order to get a bigger output, despite current setups providing the daily supply drinking water for one person.
Access to potable water remains one of the world's biggest challenges. Roughly 85 percent of the global population lives in the driest half of the planet. Over 783 million people cannot easily access clean water. These numbers are expected to grow as the global population increases. MIT mechanical engineering professor Evelyn Wang said the MOF 'sponge' could be a tremendous help.
"There are desert areas around the world with around 20 percent humidity," where potable water is a major need, she said, "but there really hasn’t been a technology available that could fill" that growing need.
Currently, countries like Chile and Morocco utilize fog harvesting. However, the process requires a pretty high moisture content -- sometimes needing a relative humidity of 100 percent. That air is also found in fewer regions than arid lands.
The full report can be found in Science journal.
While we might be several galaxies away from Uncle Owen's Tatooine moisture farm, this research brings us even closer to practical solutions to a rising problem. (However, Star Wars fans can continue to hope that they name the device a "vaporator" should it ever hit the market.)
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